1. Field of the Invention
This invention is generally directed to loudspeakers and loudspeaker systems and, more particularly, to one or more loudspeaker enclosures having horizontal cross-sections of a trapezoidal or wedge shape configuration and having horizontal curved input slots which extend between the side walls thereof wherein one or more electro-acoustic transducers are housed within each enclosure and which operate in one or more band limited frequency ranges having horizontal boundaries defined by the side walls of the enclosures such that the wavefront emitting from the transducers is converted from a circular isophase wavefront to a curved ribbon wavefront approximating the shape of a section of the surface of a toroid. The wavefronts of a plurality of enclosures form a common or continuous wavefront.
2. History of the Invention
In public and private venues, used for performance, sport, business and other applications, and in particular where people gather in large numbers, loudspeakers are generally found. Where the venue is sufficiently large and the program material demands, such loudspeakers are often found in multiples, since a single loudspeaker will often not meet the technical requirements of sound pressure, uniformity of coverage and uniformity of frequency response. These multiple groups of loudspeakers are referred to as arrays.
Most loudspeakers used in arrays are designed foremost as individual loudspeakers and perform best when used alone.
Such loudspeakers generally approximate a point source in space and form an approximate spherical radiation pattern. When applied in increasing numbers, the plurality of point sources create significant interference patterns and the quality of reproduction deteriorates significantly.
A proposed solution to this problem is presented in U.S. Pat. No. 4,862,508 which discloses "a plurality of individual sources, each of a constant directivity type." However, it can be shown that the apex of such a system is not common with the apex of the individual elements of the system and therefore represents multiple overlapping sources which create interference. It can be further shown that because the audio spectrum is very broad, typically ranging over eleven octaves or doublings of wavelength, that the physical size and spacing of the lower frequency transducers interferes with the optimal spacing and placement of the smaller high frequency transducers. Simple analysis will reveal therefore that such a system will not perform as disclosed. Indeed, several systems are currently in production and do not meet the performance criteria set forth in this patent. Such systems clearly perform as multiple source systems.
Another proposed solution is disclosed in U.S. Pat. No. 5,163,167 to Heil which utilizes a manifold or chamber to create a rectangular planar wave which results in a vertical cylindrical radiation pattern. The high frequency and mid frequency elements of the system are introduced into a common waveguide which is placed in a rectangular enclosure. Such enclosures may then be added one above another in columnar fashion, thus creating a longer vertical rectangular planar wave which will maintain its cylindrical radiation pattern. It may be said therefore that the system performs as a single unit comprised of individual pieces.
There are limits, however, to the vertical rectangular flat or planar wave approach. The cylindrical nature of the pattern fixes the horizontal beam width and the chamber design does not allow curving of the wavefront. Also, the enclosure design does not allow the curving of the whole system without creating signification gaps between enclosures which degrade system response. Further, in greater numbers, a decrease in vertical beam width occurs so that two such vertical arrays may not be placed next to each other (side by side) without creating destructive interference.
Further prior art teaches a system wherein multiple drivers in the high frequency band and the mid frequency band are introduced into a common waveguide which is placed in a single trapezoidal enclosure to provide a point source which is fed by a plurality of drivers. However, when multiples of these enclosures are arrayed in a single system, the same multiple point source destructive interference is encountered.